Inkjet printheads eject small ink droplets for printing at a desired position on a paper and print out images having predetermined colors. The most widespread technologies are based on a thermal bubble type or a piezoelectric type according to its primary working principle. The thermal bubble type employs a heater to vaporize ink droplets, and uses high-pressure bubbles to drive the ink droplets through the nozzle orifices, but has limitations in heat dispatch and its using longevity. The piezoelectric inkjet printhead has been commercialized into a bend mode and a push mode according to the deformation mechanism of the piezoelectric body. The piezoelectric type employs a forced voltage to deform a piezoelectric ceramic body, and uses flexure displacement of the piezoelectric ceramic body to change the volume of a pressure-generating chamber, thus the chamber expels an ink droplet. The piezoelectric type has superior durability and high-speed print performance, but has limitations in hybrid-system field applications and difficulties in narrowing the nozzle pitch.
The thermal and piezoelectric inkjet printheads suffer from excessive heat increment and energy consumption, and are not suitable for use in a page-width configuration. As used herein, the term “page-width” refers to printheads of a minimum length of about four inches. One major difficulty in realizing page-width inkjet printheads is that nozzles have to be spaced closely together, and the other difficulty is that the drivers providing power to the heaters and the electronics controlling each nozzle must be integrated with each nozzle. One way of meeting these challenges is to build the printheads on silicon wafers utilizing VLSI technology and to integrate complementary metal-oxide-silicon (CMOS) circuits on the same silicon substrate with the nozzles.
In order to achieve high-density nozzles and high-efficient heaters, a page-width thermal inkjet printhead with self-cooling and cavitation-immune nozzles is taught in U.S. Pat. No. 4,894,664. FIG. 1 shows a cross-section of the conventional thermal ink jet printhead. On a substrate 10, ink in an ink well 12 is evaporated by a resistor layer 14 to migrate to a nozzle area 16. A nozzle plate 18 directs the gaseous ink as it is expelled from the nozzle area 16 by pressure from the accumulated ink. A thermal barrier layer 24 prevents heat from flowing to a nickel cantilever beams 20 and a nickel substrate 22. A patterned conducting layer 26 shorts out the resistor layer 14 except on the cantilever beams 20. A protective layer 28 prevents electrical shorts during the nickel-plating process to form the nozzle plate 18. A conducting layer 29 is deposited during the manufacturing process to provide a surface upon which the nozzle plate 18 can be constructed.
An ink channel plate is a further main section of the thermal inkjet printhead. U.S. Pat. No. 5,738,799 discloses an ink jet fabrication technique that enables capillary channels for liquid ink to be formed with square or rectangular cross-sections. Particularly, a sacrificial layer of polyimide and a permanent material are applied over the main surface of a silicon chip to form open ink channels. U.S. Pat. No. 5,198,834 discloses an inkjet printer that utilizes a barrier wall located between a substrate and an orifice plate, in which ink flows through the ink channels defined in the barrier wall. The barrier wall is fabricated in two layers from cured, photo-imaged resist materials. One layer is a solder-mask material, and the other is a photolithographic resist material. The two layers together resist chemical attack by the ink and separation of the orifice plate from the printhead.
For a page-width thermal inkjet printhead, however, when the above-described ink channel fabrications using sacrificial polymer/photoresist materials are integrated with the CMOS wafer, the printhead suffers from a wafer bow effect and a fragile chamber wall, resulting in difficulties in the process being employed. Accordingly, a non-polymer ink channel and an IC compatible process of forming high nozzle density inkjet printhead with on-chip driving electronics for improved printing quality and simplified process, are called for.